1. Field of the Invention
The present general inventive concept relates to an inkjet printhead, and more particularly, to an inkjet printhead to eject ink using a piezoelectric method, and a method of manufacturing the inkjet printhead.
2. Description of the Related Art
In general, an inkjet printhead prints a predetermined color image by ejecting fine droplets of printing ink to a desired position on a print paper. The inkjet printhead can be classified into two types according to an ink ejection method: a thermal inkjet printhead and a piezoelectric inkjet printhead. The thermal inkjet printhead generates a bubble in ink using a heat source to eject the ink using an extension force of the bubble. The piezoelectric inkjet printhead uses a piezoelectric material to eject ink using a pressure applied to the ink which is generated by a deformation of a piezoelectric material.
FIG. 1 is a cross-sectional view illustrating a configuration of a conventional piezoelectric inkjet printhead. Referring to FIG. 1, a fluid path forming substrate 10 includes a manifold 13 forming a path for ink, a plurality of restrictors 12, and a plurality of pressure chambers 11. A nozzle substrate 20 includes a plurality of nozzles 22 respectively corresponding to the pressure chambers 11. A piezoelectric actuator 40 is provided in an upper portion of the fluid path forming substrate 10. The manifold 13 is a path through which ink supplied from an ink reservoir is provided to each of the pressure chambers 11. The restrictor 12 is a path through which the ink passes from the manifold 13 into each of the pressure chamber 11. The pressure chambers 11 are filled with the ink to be ejected and arranged at one side or both sides of the manifold 13. The pressure chambers 11 generate a change in pressure to eject ink out of the pressure chambers 11 or to suck the ink into the pressure chambers 11 as a pressure of the pressure chambers 11 and a volume of the ink vary according to an operation of the piezoelectric actuator 40. To this end, a portion forming an upper wall of the pressure chambers 11 of the fluid path forming substrate 10 functions as a vibration plate 14 which is deformed by the piezoelectric actuator 40.
The piezoelectric actuator 40 includes a lower electrode 41, a piezoelectric layer 42, and an upper electrode 43, which are sequentially deposited on the fluid path forming substrate 10. A silicon oxide layer 31 is formed between the lower electrode 41 and the fluid path forming substrate 10 as an insulating layer. The lower electrode 41 is formed over an entire surface of the silicon oxide layer 31 to function as a common electrode. The piezoelectric layer 42 is formed on the lower electrode 41 on an area corresponding to a location of the pressure chambers 11. The upper electrode 43 is formed on the piezoelectric layer 42 and functions as a drive electrode to apply a voltage to the piezoelectric layer 42. A flexible printed circuit 50 for supplying the voltage to the upper electrode 43 is connected to the upper electrode 43.
When a drive pulse is applied to the upper electrode 43, the piezoelectric layer 42 is deformed and the vibration plate 14 is deformed so that the volume of each of the pressure chambers 11 is changed. Thus, the ink in the pressure chambers 11 is ejected through the nozzles 22. A frequency of the drive pulse is affected by a damping performance of the piezoelectric layer 42. Therefore, a vibration of the piezoelectric layer 42 needs to be quickly dampened.
FIG. 2 is a graph illustrating a residual vibration of the conventional piezoelectric inkjet printhead of FIG. 1. Specifically, FIG. 2 illustrates a result a displacement of the piezoelectric layer 42 of FIG. 1, using laser-dopier velocimetry (LDV), after a drive pulse is applied to the upper electrode 43. Referring to FIG. 2, the displacement of the piezoelectric layer 42 to eject the ink is generated for about 15 μs and then a residual vibration of the piezoelectric layer 42 continues for about 85 μs. According to the result illustrated in FIG. 2, when a frequency of the drive pulse is greater than 10 KHz, the displacement of the piezoelectric layer 42 in a subsequent cycle is affected by the residual vibration caused by the drive pulse of the preceding cycle. As a result, it is difficult to eject ink droplets at a constant speed and a volume of the ejected ink droplets may be irregular. Also, since a pressure wave in each of the pressure chambers 11 is not removed within a short time, cross-talk can be generated between adjacent pressure chambers 11.